A large static magnetic field is used by Magnetic Resonance Imaging (MRI) scanners to align the nuclear spins of atoms as part of the procedure for producing images within the body of a patient. This large static magnetic field is referred to as the B0 field.
During an MRI scan, Radio Frequency (RF) pulses generated by one or more transmitter coils cause a called B1 field. Additionally applied gradient fields and the B1 field cause perturbations to the effective local magnetic field. RF signals are then emitted by the nuclear spins and detected by one or more receiver coils. These RF signals are used to construct the MR images. These coils can also be referred to as antennas.
MRI scanners are able to construct images of either slices or volumes. A slice is a thin volume that is only one voxel thick. A voxel is a small volume element over which the MR signal is averaged, and represents the resolution of the MR image. A voxel may also be referred to as a pixel (picture element) herein if a single slice is considered.
By performing different magnetic resonance imaging protocols (which are implemented as pulse sequences or pulse sequence commands), different types of information can be measured about a subject. For example, there are various techniques, which enable the encoding of spins such that the flow or diffusion of fluid can be directly measured. Arterial spin tagging is a technique where the spins of blood passing through a group of arteries or even single arteries can be labeled and then imaged. The reference book “Handbook of MRI Pulse Sequences” (hereafter “Handbook of MRI Pulse Sequences”) by Bersnstein et. al., Elsevier, 2004, ISBN 978-0-12-092861-3 describes in section 17.1 (pp. 802 through 829) provides a review of several different arterial spin tagging techniques.
The journal article “In Vivo Estimation of the Flow-Driven Adiabatic Inversion Efficiency for Continuous Arterial Spin Labeling: A Method Using Phase Contrast Magnetic Resonance Angiography,” O'Gorman et. al., Magnetic Resonance in Medicine 55:1291-1297 (2006) describes the combination of arterial spin labeling with an estimation of the flow-driven adiabatic inversion efficiency. Axial velocity maps are acquired using a peripherally gated 2D triggered phase contrast sequence and are acquired separately from perfusion measurements using a multi-slice CASL technique.
The journal article Wu, Wen-Chau, and Eric C. Wong. “Intravascular effect in velocity-selective arterial spin labeling: the choice of inflow time and cutoff velocity.” Neuroimage 32.1 (2006): 122-12, DOI: 10.1016/j.neuroimage.2006.03.001, discloses a velocity-selective arterial spin labeling (VS-ASL) tags spins on a basis of flow velocity, instead of spatial distribution that has been commonly adopted in conventional ASL techniques. VS-ASL can potentially generate tags that are very close to the imaging plane and whereby avoid the error source of transit delay (δt) variation independent of inflow time (TI). In practice, however, TI of VS-ASL should still be chosen with caution with respect to intravascular signal and cutoff velocity (Vc). The presented study takes advantage of multiple TI and Vc to systematically investigate the intravascular effect.
The book section Haacke, E. Mark, et al. “11.2 Continous Properties and Phase Imaging” In: Magnetic resonance imaging: physical principles and sequence design. Vol. 82. New York:: Wiley-Liss, 1999, ISBN: 978-0471351283 provides a review of phase imaging in magnetic resonance imaging.
The journal article Jensen-Kondering, Ulf, et al. “Superselective pseudo-continuous arterial spin labeling angiography.” European journal of radiology 84.9 (2015): 1758-1767, DOI: 10.1016/j.ejrad.2015.05.034, discloses the evaluation of the utility of a novel non-contrast enhanced, vessel-selective magnetic resonance angiography (MRA) approach based on superselective pseudo-continuous arterial spin labeling (ASL) for the morphologic assessment of intracranial arteries when compared to a clinically used time-of-flight (TOF) MRA.